The present invention relates to a silane coupling agent composition particularly useful in making composite materials of polyolefins, especially polyethylene.
Three types of coupling agents are used in making polyethylene composite materials. The first type of coupling agents chemically grafts to the polyolefin polymer. Vinylsilanes on fillers are known to graft to polyethylene during injection molding, and such fillers have been used in cross-linkable polyethylene insulation coverings of power cable. Mixtures of vinylsilanes with polyfunctional azides have been used to improve the strength and wet strength retention of polymers to glass, metal, and metal oxides, as described in U.S. Pat. No. 3,585,103.
The second type of coupling agents are used to treat the filler material of the composite, so the filler is more solution compatible with the polyolefin. Generally, this approach has been more effective in glassy polymers, such as polystyrene, than in crystalline polymers like polyethylene and polypropylene. The ultimate in compatibility is obtained with trimethoxysilane-modified polymer, e.g., trimethoxysilane-modified polyethylene is an effective primer for polyethylene to glass.
The third type of coupling agents are those agents which are not solution compatible with polyolefins, and generally do not chemically graft to polyolefin resins. Methacrylate functional silanes, in particular 3-methacryloxypropyltrimethoxysilane, are effective coupling agents in clay-filled polyethylene composites, as are cationic styrl-functional silanes such as 3[2(vinyl benzylamino)ethylamino]propyltrimethoxysilane. Their effectiveness is surprising, because neither silane was shown to graft to the polymer. Even amine functional silanes have been used as coupling agents for polyethylene composites with some success. Hartlein discloses that combinations of amine functional silanes and chlorinated organic compounds act as effective coupling agents and primers for polyethylene in U.S. Pat. No. 3,630,827 and U.S. Pat. No. 3,702,794. The third type of coupling agents are thought to act by forming interpenetrating polymer networks with the polyolefin.